I. Field of the Invention
The present invention relates generally to a three-wheeled motor vehicle for off-the-road use in which the three wheels have relatively wide, large-diameter, low-pressure tires, and more particularly to a vehicle of the type described having a front frame holding one steerable wheel and a driver's seat. The front frame is connected to a rear frame which supports the motor, the differential and the rear wheels in such a manner that the front and rear frames are able to be rotated relative to one another about the vehicle's longitudinal axis.
II. Discussion of the Prior Art
Various prior-art three-wheeled motor vehicles for off-the-road use are known. They generally include a front steerable wheel and two rear wheels to which the power output from the engine is applied via a suitable transmission. Each of the wheels is equipped with a relatively wide, large-diameter, low-pressure tire. Such three-wheeled vehicles are commonly used for recreational purposes, such as driving through woods and over rough terrain, but they may also be used for more utilitarian purposes, e.g., for farming, lawn care, snow removing, etc., where appropriate accessories are used therewith. The wide, low-pressure tires provide superior traction and tend not to damage the ground over which the vehicle is made to pass.
As with any three-wheeled vehicle, if an attempt is made to turn a corner at too high a speed, there is a tendency for the inboard rear wheel to lift from the ground which, when a standard differential is employed, may result in the loss of traction. Then, too, an inexperienced operator may negotiate a turn at such high speed that the tipping of the vehicle may render it unstable to the point where injury can occur to the driver if the vehicle should tip over completely.
In accordance with the present invention, the tendency of the vehicle to lose stability while cornering or when traversing uneven terrain is obviated by providing a two-piece frame assembly in which the front wheel and its associated steering mechanism as well as the rider's seat comprise a first part of the frame while the motor support platform, the two rear wheels and the associated differential comprise the second part of the frame assembly. The first and second frame assemblies are joined one to the other by way of a pivot coupling, which permits the front frame to pivot relative to the rear frame about a longitudinal axis of the vehicle. Thus, the rider, while negotiating a turn at a significant speed, may shift his center of gravity by leaning into the turn but without causing the inboard wheel to lift from the ground.
In the Winchell, et al U.S. Pat. No. 4,437,535 there is described a three-wheeled motorcycle which is constructed to have a two-piece frame construction where the front and rear portions thereof are pivotable relative to one another about a longitudinal axis. In this arrangement, the front frame, including the front steerable wheel and the operator's seat, also includes an arch-like structure which completely straddles the rear frame and the engine mounted thereon and is pivotally coupled to the front and rear ends of the rear frame at opposed ends of the arch. The vehicle described in the Winchell et al U.S. Pat. No. 4,437,535 has been designed for over-the-road use rather than off-road use. Hence, that vehicle would not expect to encounter the severe shock and vibration forces introduced upon striking obstacles, hitting uneven spots on the ground and jumping the vehicle wherein at times all three wheels may be off the ground. The present invention has been designed with that more severe use in mind.
In accordance with the invention, a three-wheeled motor vehicle is constructed to have a rocking frame comprised of a front frame member including a steering front wheel and a riding seat which is free to rock laterally with respect to the direction of travel and with respect to a rear frame member which supports the engine and the rear wheels driven thereby. Considering the rough terrain and riding conditions, it is imperative that the overall frame be solidly constructed, especially in the way that the front frame member and the rear frame member are joined together for relative movement therebetween.